The KDE screensavers, while able to be previewed/tested, don't launch upon time out - the screen is blank. I know this is a problem for a large number of users running Fedora Core 3 and other distributions.

I have seen some solutions posted suggesting 'xscreensaver' instead, but was wondering if anyone knows the cause and solution to this problem?

As usual the problem is that when you do not know why it does not work... it is the file rights. I had the same problem as I changed profile for root to umas 077.

So make a rpm -qa |grep screensaver
then a rpm -ql ....sometghing screensaver packages...
look what directory are mentionned. for me on 2 direcotries the rights were 700 so KDE user could not enter to that directory and xscreensaver did not work...